(Newser)
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A 4-year-old girl in Oregon has died after being stricken with E. coli, and her 5-year-old friend remains hospitalized, reports Q13 Fox. Authorities are awaiting lab results that might help determine how Serena Faith Profitt of Otis got sick, though they say they may never zero in on the exact source, reports AP. Two possibilities: The pair shared a turkey sandwich at a restaurant over the Labor Day weekend, and they swam together in a pond the weekend before that, reports the Oregonian. A check of the restaurant has raised no red flags, however, and nobody else who swam in the pond has gotten sick.

"Our investigation is ongoing," says a health official in Lincoln City. "There's a lot of field work, then there's a lot of waiting." Serena fell ill and eventually suffered kidney failure and brain damage. At one point, she was released from the hospital, only to return in worse shape. Her family tells KATU that the hospital failed to run tests that would have diagnosed E. coli and might have saved her, and they are planning legal action. Meanwhile, Serena's friend, 5-year-old Brad Sutton, is showing signs of improvement. "His levels for his kidneys are coming up ... but he’s not out of the woods," says his mom.